1. Field of the Invention
The present invention relates to a method for transmitting digital audio signals from recording studios to various master stations of a broadcasting network.
2. Description of the Prior Art
For projected future digital broadcasting systems it will be necessary to transmit a multiplicity of individual programs from the various recording studios of the broadcasting corporations to the individual master stations of these broadcasting networks, which are planned on a country-wide basis.
The so-called DAB network (Digital Audio Broadcasting, described in "Digital Audio Broadcasting" ITU-COM 89, Geneva, October 1989, and in "Kunftige Systeme der digitalen Horfunkubertragung", Bayerischer Rundfunk, November 1990, both incorporated herein by reference) provides, for example, simultaneous broadcasting networks in which every DAB station transmits a plurality of digital audio signals, e.g. 6 stereo signals, in clock-synchronous and word-synchronous, i.e. bit-synchronous fashion, in a so-called COFDM signal (Coded Orthogonal Frequency Division and Multiplexing). Since a country may have a plurality of separate radio service areas, there results a large number of programs which must be fed to the DAB network of the service area or country, respectively. Assuming that there are four frequencies which are provided for simultaneous broadcasting networks, and further assuming that a big country comprises 10 networks each comprising six programs, this already totals 60 programs. Even if the known and technically mature so-called DS1/DSR satellite transmission were used for distributing the audio signals from the recording studios to the various master stations of the broadcasting network, the transmission would be limited to only 16 programs for each DSR channel, which would be insufficient for modern country-wide broadcasting networks with regional service.
With the so-called DS1 technique (Digital Sound 1 Mbit/s), two audio signals or, respectively, a stereo signal and additional information, are transmitted in a serial stream. A scale factor is introduced for data reduction (European Patent Application 0 133 697 and paper "Audio-Coder DCA fur den digitalen Horfunk" in "Neues yon Rohde & Schwarz", No. 114, summer of 1986, pages 13-10, both incorporated herein by reference). 16 of these DS1 audio signals generated by a DS1-coder are then interlaced through a data multiplexer on the basis of the so-called DSR technique (Digital Satellite Radio), and are supplied in a 4-PSK-modulator for instance to a satellite earth station ("Neues yon Rohde & Schwarz", No. 114, page 14). The satellite transmitter transmits for example at 18 GHz to the satellite which in turn transmits at 12 GHz to the individual consumer satellite receivers. From the 4-PSK-demodulated digital stream the desired audio signals can be selected from a total of up to 16 digital audio signals through a demultiplexer/decoder, and can be made audible after digital-to-analog conversion.
For transmitting the digital audio signals from the recording studios to the master stations of a broadcasting network it has already been proposed to make use of the satellite transmission technique (Rohde & Schwarz study on "Program and Data Lines to VHF-FM-Transmitters", October 1990). But even a combination of the above-described DS1-DSR broadcasting techniques, which is quite common today, with such a satellite transmission technique would again result in a maximum of 16 programs per each DSR channel being transmitted from the recording studios to the various master stations of the broadcasting network, which is quite insufficient as has been explained above.